1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a method of generating mask data in fabricating semiconductor devices. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for suppressing a proximity effect in mask fabrication.
2. Discussion of the Related Art
In a photolithographic process of the semiconductor fabrication, a photoresist is patterned by exposing the photoresist to light through a mask on a semiconductor substrate. The semiconductor substrate is then etched using the patterned photoresist. In order to form a contact hole or a via hole in the semiconductor substrate, it is imperative to pattern the photoresist without shifting hole locations and distorting a hole shape.
As a semiconductor device becomes highly integrated, a distance between contact holes and via holes becomes narrower, so that a distance between holes in a mask hole pattern is inevitably closer. Accordingly, as the distance between holes in a mask having a hole pattern becomes closer, a photoresist hole pattern distorted from the original mask hole pattern may be formed on the semiconductor substrate surface due to a proximity effect.
The proximity effect occurs when a photoresist is exposed to light, and a hole pattern on a semiconductor substrate tends to be larger than the original mask hole pattern. The light which has passed through the hole in a mask exists not only in a lower portion of the hole but also in a lower portion of the region other than the hole. This is due to its wave characteristic, wherein the light existing in lower portions of the hole as well as the region other than the hole develops a constructive interference. When an intensity of the constructively interferenced light is high enough to etch the photoresist, the photoresist is further etched an area around the original mask hole pattern, thereby deviating from the mask hole pattern. In this process, a distortion of the photoresist hole pattern from the mask hole pattern becomes larger as the distance between holes becomes closer.
FIGS. 1A through 1C are top views of hole patterns to illustrate a proximity effect. In each drawing, a mask hole pattern 1 is shown as a solid line while a photoresist hole pattern 2 formed on a semiconductor substrate is shown as a dotted line. Since a contact hole or a via hole is formed as a square column, the mask hole pattern 1 is formed as a square shape.
FIG. 1A shows an example for which a mask having a single hole assuming that a distance between holes is infinite, so that the photoresist is etched by only an intensity of the light passed through the hole. In other words, a constructive interference plays no role in this case. Therefore, the photoresist hole pattern 2 formed on the semiconductor substrate is the same as the mask hole pattern 1.
In FIG. 1B, however, the mask hole pattern 1 has neighboring holes having a distance therebetween, so that the photoresist hole pattern 2 formed on the semiconductor substrate is further etched by a distance d due to a proximity effect. As a result, the photoresist hole pattern 2 formed is rectangular instead of square and extends in a direction toward a neighboring hole direction.
FIG. 1C shows a distance between holes which is much narrower than that of FIG. 1B. The photoresist hole pattern 2 formed on the semiconductor substrate is shifted by a distance d', which is larger than d in terms of a shifted degree from the mask hole pattern 1. Thus, the holes 2 are connected to one another, as shown in FIG. 1C.
In order to prevent the proximity effect, a phase shift mask or an anti-reflective film has been employed in a background art. The phase shift mask has a controlled thickness and material in a light-shielding region to invert the phase of light in the light-shielding region of the phase shift mask. That is, the phase shift mask prevents a proximity effect by offsetting the light in a lower portion of the region other than the hole. However, since such a phase shift mask is expensive, it cannot be widely applied in the general process.
In another method of the background art, after an anti-reflective film is coated under the photoresist, the photoresist is patterned using a general mask. In this process, the anti-reflective film causes respective light on a lighting region and a shielding region to have opposite phases and to be offset with each other. Nonetheless, such a method still requires a coating process of the anti-reflective film.